Electrostatic discharge (ESD) is defined as a sudden and momentary electric current that flows between objects. ESD occurs when there is a significant electrical potential difference in between two objects. ESD may occur through a direct contact or through an electrostatic field induction. ESD is a common problem in a semiconductor industry and poses a serious threat to integrated circuits (ICs) in particular. ICs may suffer permanent damage when subjected to the relatively high voltages that occur during ESD events. As a result, there are now a number of ESD protective devices that help to prevent permanent damage.
The circuitry commonly used to protect ICs during an ESD event is an ESD transistor. The ESD transistor only permits a constant current between input and output (TO) paths. Such feature of only permitting a constant current provides protection against damages to the IC in the event of ESD. The ESD transistor functions like a ballast resistor towards the ESD current. In the event of ESD, the ballast resistor provides protection to critical circuitries within the ICs.
As the IC industry moves from one process node to another, the ESD transistor has moved from a design to another design accordingly. At different process nodes, different design rules are applicable. The ESD transistor designs that work on a former process might not work for a different process node. In addition, for newer generation process nodes, the distance in between structures within the IC continues to shrink. Ballast resistance is a function that depends on distances the ESD current propagates on the ballast resistor. The ballast resistor design from the older process generation, typically, may not function as effectively on the newer generation process. As the ESD transistor structure shrinks, the ballast resistance effectiveness decreases and the ESD transistor may be unable to be placed in a smaller node.
It is within this context that the embodiments described herein arise.